Wireless communications devices are an integral part of society and permeate daily life. The typical wireless communications device includes an antenna, and a transceiver coupled to the antenna. The transceiver and the antenna cooperate to transmit and receive communications signals.
One particularly advantageous antenna type is the phased array antenna. The phased array antenna comprises a plurality of antenna elements, and processing circuitry to vary the related phase of the signals received from the individual antenna elements. The varying of the related phase of the antenna elements may provide for changing the effective radiation pattern of the antenna. In particular, the radiation pattern can be changed to be highly directional, i.e. reinforcing signals received from one direction and rejecting those received from other directions. Each directional pattern is commonly described as a beam, and the changing of the directional pattern is known as beam forming.
Beam forming operations may be performed either in the analog domain or in the digital domain. For example, in the analog approaches, the phased array antenna includes some form of time delay mechanism downstream from the antenna elements. In digital beam forming applications, the signal from the antenna element is converted into a digital signal, and digital signal processors perform the time delay operations.
As the operational frequency of the phased array antenna increases, the physical size of the individual antenna element becomes smaller. Moreover, the computational requirements for digital beam forming may become onerous. Indeed, as the space between antenna elements becomes constrained, the packaging size for processing components for each antenna element must be reduced. For example, millimeter wave, i.e. extremely high frequency (EHF), phased array antennas may be complex and costly to manufacture. Furthermore, these phased array antennas may be limited in bandwidth and the number of beams.
One approach to the phased array antenna is disclosed in U.S. Pat. No. 5,999,128 to Stephens et al. This phased array antenna includes a plurality of antenna elements, and a plurality of optical paths with varying lengths coupled to the respective antenna elements. The phased array antenna comprises a plurality of phase coherent sources, and a plurality of combiners coupled downstream for the phase coherent sources for providing a signal to the optical paths.